Nonlinear Dynamic Analysis Of Hydrodynamic Journal Bearings Allowing For Roundness Error

Hydrodynamic journal bearings are widely used in power engineering and aerospace engineering. Stability and dynamic characteristics of a hydrodynamic journal bearing system have a close relationship with the system structure parameters. Most of the researche on dynamic of hydrodynamic journal bearings is according to the design dimension without considering the influence of manufacturing tolerances. Actually, all kinds of manufacturing errors of structure parameters affect the dynamic characteristics in different degrees. Manufacturing errors exist objectively. Thus, the manufacturing errors'effects on dynamic characteristics can't be ignored. The main purpose of this study is to discover the influences of roundness error on hydrodynamic journal bearings'dynamic stability.First, an oil-film force model of a hydrodynamic journal bearing allowing for roundness error is established. Then, the oil-film force can be solved from the Reynolds equation with the finite difference method, and the journal's displacements at any instant can be calculated based on Newton's law. After that, the axis orbits of journal center can be drawn with the displacements. And the critical speed of the hydrodynamic journal bearing can be calculated relative to whether the axis orbits are convergent or divergent. Finally, the stability map can be plot using the dimensionless parameter op, which was first proposed by Professor Xu Wubin.In the last chapter of this paper, twenty-two group experiments were done. The results show good corrletation between the experimental data and the stability map of hydrodynamic journal bearings with different roundness errors, but there are some discrepanies. Conclusions may be drawn from this research as follows: the roundness error of a journal affects the dynamic stability obviously. And the critical speed increases with roundness error when the eccentricity ratio is less than 0.5. But the critical speed decreases with roundness error when the eccentricity ratio is greater than 0.7. The critical speeds have little difference between journals with and without roundness error when eccentricity ratio is between 0.5 and 0.7.The results can be used to guide designing hydrodynamic journal bearings'structure parameters, and also can be used to evaluate whether a bearing is at a stable or an unstable state.